Augmented whole-body scanning via magnifying PET (AWSM-PET) is a technology that aims to enhance the image resolution and sensitivity of the clinical PET/CT scanner for whole-body imaging. This study presents the system design, performance evaluation, and results from phantoms and initial human imaging studies. Methods: The AWSM-PET system integrates 2 high-resolution detector panels ("outserts") with a Biograph Vision PET/CT scanner (Siemens Healthineers). Positioned outside the scanner's axial field of view, each panel consists of 32 detector modules, each containing a 30 × 30 lutetium oxyorthosilicate crystal array (0.97 × 0.97 × 10 mm³ per crystal) at 1.05-mm pitch. These detectors are packaged and read out using the scanner's detector electronics assembly. Customized firmware and software were developed to establish the additional coincidence detection among the outserts and the scanner. The system acquires data simultaneously during a whole-body scan using continuous bed motion. List-mode-based image reconstruction software has been developed for AWSM-PET system using the continuous-bed-motion protocol. Performance was evaluated through sensitivity measurements, imaging of a mini-resolution phantom containing multiple groups of hot spheres, a National Electrical Manufacturers Association Image Quality (NEMA IQ) phantom study with custom small-diameter tumor inserts, and an initial human study. Results: The outsert detectors achieved an energy resolution of 11% at 511 keV. The coincidence resolving time between the outserts and between outserts and scanner was 183 and 211 ps full width at half maximum, respectively. Sensitivity increased by up to 18.4%, depending on the source location. Mini-resolution phantom images demonstrated higher peak-to-valley ratios for spheres with a diameter of 6 mm or less compared with native scanner images. In the NEMA IQ study, AWSM-PET achieved a higher contrast recovery ratio (CRC) for the smallest spheric lesion (diameter, 4.88 mm) across all CRC metrics (maximum, peak, and mean) but no improvement for larger lesions compared with high-resolution Biograph Vision images. Initial human imaging confirmed the system's compatibility with clinical workflows, achieving improved resolution in high-count regions, such as the brain. However, increased noise in low-count regions (e.g., abdomen) was observed and requires further improvement. Conclusion: The prototype AWSM-PET system demonstrated enhanced image resolution and sensitivity of a clinical PET/CT scanner without negatively impacting its performance, showing improved CRC and spatial resolution for small lesions in phantom and human imaging.

Objective. Modern PET scanners offer precise TOF information, improving the SNR of the reconstructed images. Timing calibrations are performed to reduce the worsening effects of the system components and provide valuable TOF information. Traditional calibration procedures often provide static or linear corrections, with the drawback that higher-order skews or event-to-event corrections are not addressed. Novel research demonstrated significant improvements in the reachable timing resolutions when combining conventional calibration approaches with machine learning, with the disadvantage of extensive calibration times infeasible for a clinical application. In this work, we made the first steps towards an in-system application and analyzed the effects of varying data sparsity on a machine learning timing calibration, aiming to accelerate the calibration time. Furthermore, we demonstrated the versatility of our calibration concept by applying the procedure for the first time to analog readout technology. Approach. We modified experimentally acquired calibration data used for training regarding their statistical and spatial sparsity, mimicking reduced measurement time and variability of the training data. Trained models were tested on unseen test data, characterized by fine spatial sampling and rich statistics. In total, 80 decision tree models with the same hyperparameter settings, were trained and holistically evaluated regarding data scientific, physics-based, and PET-based quality criteria. Main results. The calibration procedure can be heavily reduced from several days to some minutes without sacrificing quality and still significantly improving the timing resolution from ( 304 ± 5 ) ps to ( 216 ± 1 ) ps compared to conventionally used analytical calibration methods. Significance. This work serves as the first step in making the developed machine learning-based calibration suitable for an in-system application to profit from the method’s capabilities on the system level. Furthermore, this work demonstrates the functionality of the methodology on detectors using analog readout technology. The proposed holistic evaluation criteria here serve as a guideline for future evaluations of machine learning-based calibration approaches.

The Augmented Whole-body Scanning via Magnifying PET (AWSM-PET) is a technology designed to enhance the diagnostic accuracy of whole-body (WB) PET/CT imaging for the detection of small lesions. We recently constructed the first prototype AWSM-PET device that consists of two panels of high-resolution time-of-flight (TOF) PET detectors (using ~1mm pitched LSO crystals), integrated with the standard readout electronics and event processing architecture of the Siemens Biograph Vision scanner. The system exhibits excellent spatial, energy and timing resolution, with an average coincidence resolving time of ~183 ps FWHM and an average energy resolution of ~11% FWHM at 511 keV. Custom firmware and software have been developed to encode the large number of detector elements and to enable coincidence detection between the AWSM-PET detectors and the Biograph Vision scanner.Initial tests of the AWSM-PET device show the image resolution of the Biograph Vision scanner is improved from the original >3mm to ~2mm FWHM. A GPU-based list-mode image reconstruction framework has been expanded to incorporate the point-spread function (PSF) of the native scanner and the AWSM-PET detectors to optimize the spatial resolution and improve image quality.Standard step-and-shoot and continuous-bed motion imaging protocols are supported for the AWSM-PET operation and are being evaluated for the reconstructed image resolution and the uniformity of the overall system sensitivity across a long axial FOV. Extensive phantom imaging studies are ongoing to evaluate the system's performance. Initial human imaging studies will be presented in the upcoming 2023 Medical Imaging Conference.

Last year’s SNMMI, Siemens Healthineers presented the Biograph Vision.X PET/CT scanner, currently delivering the industry’s leading time-of-flight (TOF). Although recent TOF-research explores novel materials, electronics, and calibration concepts, system developments are often evaluated against the Biograph Vision.X benchmark. In this work, we explored what coincidence time resolution (CTR) can be achieved with conventional readout electronic (TOFPET2c ASIC) and clinical detector blocks using our previously established residual physics timing calibration. It is the first time we apply the concept to a detector read out with analog SiPMs and the TOFPET2c ASIC. Our method relies on channel-individual information in combination with machine learning (ML) models, which we characterized in this work regarding their functionality and capability to improve the detectors’ CTR. We compare the timing performance against an approach based on a purely analytical calibration as it is applicable to general system architectures. The results show that the residual physics calibration concept offers significant advances demonstrated by the improvement of CTR from $335 \pm 5 \mathrm{ps}$ (analytical cal) to around $219 \pm 1 \mathrm{ps}$ (analytical cal + ML) for coincidences within an energy window from 300 keV to 700 keV.

A novel technique, called augmented whole-body scanning via magnifying PET (AWSM-PET), that improves the sensitivity and lesion detectability of a PET scanner for whole-body imaging is proposed and evaluated. A Siemens Biograph Vision PET/CT scanner equipped with one or two high-resolution panel-detectors was simulated to study the effectiveness of AWSM-PET technology. The detector panels are located immediately outside the scanner's axial field-of-view (FOV). A detector panel contains 2 × 8 detector modules each consisting of 32 × 64 LSO crystals (1.0 × 1.0 × 10.0 mm 3 each). A 22 Na point source was stepped across the scanner's FOV axially to measure sensitivity profiles at different locations. An elliptical torso phantom containing 7 × 9 spherical lesions was imaged at different axial locations to mimic a multi-bed-position whole-body imaging protocol. Receiver operating characteristic (ROC) curves were analyzed to evaluate the improvement in lesion detectability by the AWSM-PET technology. Experimental validation was conducted using an existing flat-panel detector integrated with a Siemens Biograph 40 PET/CT scanner to image a torso phantom containing spherical lesions with diameters ranging from 3.3 to 11.4 mm. The contrast-recovery-coefficient (CRC) of the lesions was evaluated for the scanner with or without the AWSM-PET technology. Monte Carlo simulation shows 36%-42% improvement in system sensitivity by a dual-panel AWSM-PET device. The area under the ROC curve is 0.962 by a native scanner for the detection of 4 mm diameter lesions with 5:1 tumor-to-background activity concentration. It was improved to 0.977 and 0.991 with a single- and dual-panel AWSM-PET system, respectively. Experimental studies showed that the average CRC of 3.3 mm and 4.3 mm diameter tumors were improved from 2.8% and 4.2% to 7.9% and 11.0%, respectively, by a single-panel AWSM-PET device. With a high-sensitivity dual-panel device, the corresponding CRC can be further improved to 11.0% and 15.9%, respectively. The principle of the AWSM-PET technology has been developed and validated. Enhanced system sensitivity, CRC and tumor detectability were demonstrated by Monte Carlo simulations and imaging experiments. This technology may offer a cost-effective path to realize high-resolution whole-body PET imaging clinically.

In this work we evaluate PET detector prototypes which combine and surpass the HRRT and BrainPET detector capabilities. Our goal is to assess the feasibility of constructing higher performance brain PET systems. Several different geometries of detectors were investigated. Detector modules comprising a 5 × 5 or 10 × 10 array of 3.2 × 3.2 × 20 mm 3 or 1.6 × 1.6 × 15 mm 3 LSO crystals, respectively, were read out by a 4 × 4 element array of silicon photomultipliers. Such detector configurations do not allow depth-of-interaction determination, but provide excellent spatial and coincidence timing resolution of 192 ps and 214 ps FWHM, respectively. Two other configurations with depth-of-interaction capability were constructed. The simplest realization consists of 5 × 5 air coupled LSO crystals, 3.2 × 3.2 × 10 mm 3 in size, arranged in two stacked layers. The crystals of the top and bottom layers were selected to differ by their light outputs and decay times. The second is a triple layer detector built with a bottom layer of 4×4 elements, 4 × 4 × 10 mm 3 in size, a middle layer of 6 × 6 elements, 2 × 2 × 10 mm 3 in size, and a top layer of 5 × 5 elements, 2 × 2 × 10 mm 3 in size. The triple layer detector had 3M ESR foil in between the pixels to enhance pixel separation. To understand how the pixelation influenced our timing results single continuous LSO blocks 16 × 16 × 20 mm 3 and 16 × 16 × 16 mm 3 in size were also tested.

A previously developed method derives co-registration parameters from PET and CT images of a four-point-source calibration phantom by manually adjusting the offsets and orientation of the CT image to achieve alignment with the PET image in a graphic viewer. This manual process is tedious and can be inaccurate, especially when rotational offsets exist. An automated segmentation method has been developed, based on thresholding and application of constraints on the sizes of point sources in the images. After point sources are identified on PET and CT images, co-registration is performed using an analytic rigid-body registration algorithm which is based on singular value decomposition and minimization of the co-registration error. The co-registration parameters thus derived can then be applied to co-register other PET and CT images from the same system. Twenty PET-CT images of the calibration phantom at various locations and/or orientations were obtained on a Siemens Inveon® Multi-Modality scanner. We tested the use of from 1 to 10 data sets to derive the co-registration parameters, and found that the co-registration accuracy improves with increasing number of data sets until it stabilizes. Co-registration of PET-CT images with an accuracy of 0.33±0.11 mm has been achieved by this method on the Inveon Multi-Modality scanner.

We recently reported a numerical ray-tracing algorithm for calculating the point-spread function (PSF) used in 3-D ordered subsets expectation maximization (OSEM) reconstruction of single and multi-pinhole collimated single photon emission computed tomography (SPECT) images. In this work, we evaluated the performance of our PSF reconstruction method with and without X-ray CT-based attenuation correction (AC) and dual energy window scatter correction (SC). X-ray CT data was acquired to create the attenuation maps. SPECT data was acquired using 99mTc phantoms and 5-pinhole tungsten collimators with 1.0 mm diameter pinholes. With no corrections applied, an axial image slice of a 3 cm diameter cylinder uniformly filled with mTc showed a 13% dip near the center of the phantom. When AC and SC were applied, the cross-section through an axial slice showed a desirable flattened profile that dipped only 3%. We also scanned a mouse with 99mTc implantable sources that had negligible self-attenuation. The sources were first scanned in air for calibration. Our results show that the reconstructed SPECT images with no corrections underestimated the activity for each mTc implanted source by 12% on average, while the image with AC and SC underestimated the activity by only 3.3% on average. We repeated all of the experiments with 125I phantoms but did not apply SC to the 125I data. With no correction applied, an axial slice of a 3 cm diameter cylinder uniformly filled with 125I dipped 25 % near the center of the phantom. After applying AC, the 125I image profile no longer dipped but rather was overcorrected by 4.5%. Similarly, the reconstructed image of the 125I implants with no correction underestimated the activity of each source by 23% on average, while the 125I image with AC overestimated the activity in the sources by 4.6% on average. These results have shown that our PSF- - reconstruction method with CT-based attenuation correction improved the quantitative accuracy of SPECT images for representative 99mTc and 125I studies.

The Quicksilver event processing module (EPM) designed for the Siemens Inveon Dedicated PET (Positron Emission Tomography) preclinical scanner, has been leveraged in the development of a new SPECT (Single Photon Emission Computed Tomography) EPM module. This new module is used in Inveon SPECT systems and provides 16 channels of high speed data acquisition and event processing functions. Fifteen of these channels are used for processing 7 X signals, 7 Y signals and a SUM signal all received from the SPECT detector electronics. Custom mixed-signal CMOS ASICs and high speed ADCs are utilized to provide the front-end analog portion of the data acquisition. A high performance FPGA provides the digital portion of the data acquisition running at 100 MHz and the subsequent event processing. This FPGA also provides multiple high speed serial data channels for external interconnection. These interconnections allow the module to be replicated as needed in a distributed parallel processing architecture for flexible, high performance SPECT imaging. The module also provides controllable high voltage needed to bias the SPECT detectors. A four head Nal(Tl) based SPECT system is currently being built using one SPECT EPM per SPECT head.

Multi-pinhole SPECT collimators can provide sub-millimeter resolution and improved sensitivity over single-pinhole and parallel-beam collimators. Attenuation and scatter will degrade the quantitative accuracy of reconstruction for lower energy emitters like I-125 and therefore both effects should be accounted for during reconstruction. We implemented an OSEM MAP reconstruction which incorporated attenuation, scatter and detector intrinsic resolution for a multi-pinhole detector designed for whole-body mouse imaging. The ray- driven projector/backprojector implemented considerably reduced the calculation of attenuation factors and decreased reconstruction time compared to a voxel-driven approach. The multi-pinhole SPECT system simulated consists of 2 or 4 cameras, with a 5-pinhole collimator plate for each. The attenuation map would be obtained from a CT system mounted on the same gantry. Scatter is estimated from scatter windows using a triple energy window (TEW) method and applied during the iterative reconstruction. A quadratic smoothness prior is implemented to control noise. Simulations with the MOBY mouse phantom show that modeling of the pinhole sensitivity, attenuation and detector intrinsic resolution results in a more accurate reconstruction. Preliminary Monte Carlo simulations showed the importance of determining and correcting the attenuation and scatter for I-125 imaging. Further investigations will be performed towards accurate estimation of the point-spread-function or sensitivity model of the multi-pinhole collimator plate.

The quicksilver event processing module (EPM) is a key component of a high performance data acquisition platform from Siemens Molecular Imaging (Knoxville, TN) for use in the Inveontrade line of multimodal PET and SPECT preclinical imaging systems. The card's main purpose is to condition, digitize and process incoming analog pulses from PMT or APD based PET or SPECT detectors. Analog pulses from a detector are digitized using a 100 MHz continuous sampling ADC and read into a Xilinx Virtex II Pro FPGA for processing. The FPGA performs digital integration, baseline offset correction and pileup rejection. Because these functions are done in the digital domain, different algorithms can be quickly re-implemented and tested. The EPM has the ability to capture raw event ADC samples, allowing for the quick development and comparison of new algorithms in software on actual event samples. The Inveontrade small animal PET scanner uses a larger LSO block detector and new analog front end than previous generation scanners which increases the likelihood of pileup events. The digital pulse processing methods presented here have been evaluated to obtain the best energy and positioning performance from the high pixel count Inveontrade detectors while maintaining high stability across countrates.

The gamma-ray detector developed for the Siemens Inveontrade small animal PET systems affords improved light collection and reduced number of photodetectors, while providing 67% greater axial field of view over the previous Focustrade system design. This is achieved using a tapered, multiple-element lightguide to couple the detector's 1.6 mm pitch, 20 times 20 LSO crystal array (32 mm square) to the 23.5 mm square photosensitive area of a Hamamatsu R8900 C12 PSPMT. The response of 900 production detectors to 511 keV photons has been analyzed. The average peak-to-valley ratio of crystal rows and columns derived from 2-d event position histograms was 4.08 plusmn 0.26 (plusmn1 SD; range of 2.96 to 5.60), and the average detector energy resolution derived from individual crystal spectra was 12.3 plusmn 0.5% FWHM (plusmn1 SD; range of 11.2% to 13.9%). Application of this compact detector in conjunction with the Quicksilvertrade electronics architecture enables flexible system design for high performance PET imaging.

Sentinel lymph node (SLN) biopsy is now standard practice in the management of many breast cancer patients. Localization protocols vary in complexity and rates of success. The least complex involve only intraoperative gamma counting of radiotracer uptake or intraoperative visualization of blue-dye uptake; the most complex involve preoperative gamma imaging, intraoperative counting and intraoperative dye visualization. Intraoperative gamma imaging may improve some protocols. This study was conducted to obtain preliminary experience and information regarding intraoperative imaging. Sixteen patients were enrolled: 8 in a protocol that included intraoperative counting and dye visualization (probe/dye), 8 in a protocol that involved intraoperative imaging, counting and dye visualization (camera/probe/dye). Preoperative imaging of all 16 patients was performed using a GE 500 gamma camera with a LEAP collimator (300 cpm/muCi). The results of this imaging were not, however, given to the surgeon until the surgeon had completed the procedures required for the study. A Care Wise C-Trak probe was used for intraoperative counting. A Gamma Medica Inc. GammaCAM/OR (12.5 x 12.5 cm FOV) with a LEHR collimator (135 cpm/muCi) was used for intraoperative imaging. Times from start of surgery to external detection of a radioactive focus and to completion of excision of SLNs were recorded. Foci were detected preoperatively via imaging in 16/16 patients. Intraoperative external detection using the probe was accomplished in less than 4 min (mean = 1.5 min) in 15/16 patients, and via intraoperative imaging in 6/8 patients. The average time for completion of excision of nodes was 19 min for probe/dye and 28 min for camera/probe/dye. In one probe/dye case, review of the preoperative images prompted the surgeon to resume axillary dissection and remove one additional SLN.

A new detector for single photon emission computed tomography (SPECT) has been developed for the Siemens microCATreg II and Inveon Multimodality preclinical imaging systems. The detector provides an active imaging area of 15 cm times 15 cm. We review the design of this new SPECT detector and present some key performance characteristics. Integral and differential uniformity were 3.7% and 3.0%, respectively. Mean energy resolution for 99mTc (140 keV) was 12.5%. Sensitivity as high as 1400 cps/MBq was measured for 99mTc on a dual-detector system, and a spatial resolution of 0.7 mm (FWHM) was obtained using 0.5 mm single pinhole collimators. Additionally, we present data from representative preclinical SPECT studies acquired with single and multi-pinhole collimators and multiple isotopes. Reconstructed images demonstrate that this detector is capable of high-resolution SPECT for multimodality small animal imaging.